1. Field of the Invention
The present invention relates to an image display apparatus having a plurality of image forming devices.
2. Description of the Related Art
There are known two types of electron-emitting devices: a hot cathode device and a cold cathode device. For example, as cold cathode devices, a field emission type (hereinafter referred to as “FE type”) of device, a metal/insulator/metal type (hereinafter referred to as “MIM type”) of electron-emitting device, a surface conduction type of electron-emitting device are known.
A surface conduction electron-emitting device is simple in structure and can be easily manufactured. Therefore it has the advantage of constituting an array in which a multiplicity of devices are formed over a large area. Methods for arranging a multiplicity of devices and driving the devices, e.g., one disclosed in JP 64-3132 A are being studied. For example, as applications of surface conduction electron-emitting devices, image forming apparatuses such as image display apparatuses and image recording apparatuses, charged beam sources, etc., are being studied.
In particular, image display apparatuses, such as those disclosed in U.S. Pat. No. 5,066,883 B and JP 2-257551 A are which use a combination of a surface-conduction electron-emitting device and a phosphor capable of emitting light when irradiated with an electron beam, are being studied for application of surface conduction electron-emitting devices. It is expected that image display apparatuses using a combination of a surface conduction electron-emitting device and a phosphor will have improved characteristics in comparison with the other types of conventional image display apparatuses. For example, even in comparison with liquid crystal displays which have recently come into widespread use, image display apparatuses using a combination of a surface conduction electron-emitting device and a phosphor are more advantageous because they can be used without a backlight and have a wider viewing angle.
FIG. 14 shows a multi-electron source formed by using an electrical wiring method. The multi-electron source shown in FIG. 14 has a multiplicity of surface conduction electron-emitting devices provided as image forming devices and which are arranged two-dimensionally, and wiring which connects these devices in matrix form. In FIG. 14, reference numeral 4001 represents the surface conduction electron-emitting devices shown schematically, lines in row wiring (scanning wiring) are indicated by 1003, and lines in column wiring (modulation wiring) are indicated by 1004. Each of row wiring lines 1003 and column wiring lines 1004 actually has a finite electrical resistance, which is shown in the figure as a wiring resistance 4004 or 4005. Wiring such as that shown in FIG. 14 is called passive matrix wiring.
Surface conduction electron-emitting devices used as electron-emitting devices 4001 are generally divided into planar-type devices and vertical-type devices. A planar-type device is constructed in such a manner that a pair of device electrodes formed as a cathode electrode and a gate electrode are disposed substantially horizontally and the direction of emission of electrons from the device is approximately perpendicular to the horizontal surface of the device. A vertical-type device is constructed in such a manner that a cathode electrode and a gate electrode are disposed substantially vertically and the direction of emission of electrons is generally parallel to the vertical plane.
A conductive thin film is formed between the cathode electrode and the gate electrode. When an device current is caused to flow through the path between the pair of electrodes, electrons are emitted from electron emitting portions which are fine fissures formed in the thin film. The conductive thin film is formed of a material selected from various materials, for example, metals, such as Pd, Pt, Ru, Ag, Au, Ti, In, Cu, Cr, Fe, Zn, Sn, Ta, W, and Pb; oxides, such as PdO, SnO2, In2O3, PbO, and Sb2O3; borides, such as HfB2, ZrB2, LaB6, CeB6, YB4, and GdB4; carbides, such as TiC, ZrC, HfC, TaC, SiC, and WC; nitrides, such as TiN, ZrN, HfN; semiconductors, such as Si and Ge; and carbon.
Needless to say, the scale of the matrix is not limited to that of the 6×6 matrix which is illustrated for the sake of convenience. For example, in the case of a multi-electron source for an image display apparatus, a certain number of devices for display of the desired image are arranged and wired. In a multi-electron source having surface conduction electron-emitting devices wired by passive matrix wiring, suitable electrical signals are applied to row wiring 1003 and column wiring 1004 to output desired electron beams. FIGS. 15A to 15D show examples of drive waveforms for driving surface conduction electron-emitting devices in a matrix.
FIG. 15A shows the voltage waveform of a selected potential applied to a selected row wiring line, FIG. 15B shows the voltage waveform of a modulation signal applied to a column wiring line, FIG. 15C shows the voltage waveform applied to a selected device, and FIG. 15D shows the voltage waveform applied to an unselected device.
Referring to FIG. 14, a selected potential Vs is applied to the row wiring line 1003 corresponding to one of the rows selected, while a non-selected potential Vns is applied to the row wiring lines 1003 corresponding to the rows unselected. In synchronization with the application of these potentials, a modulation signal Ve for outputting an electron beam is applied to each of the column wiring lines 1004. With this method, if the voltage drops due to the wiring resistances 4004 and 4005 are ignored, a voltage Ve−Vs, which is the potential difference between the selected potential and the potential of the modulation signal, is applied to the surface conduction electron-emitting devices in the selected row, while a voltage Ve−Vns, which is the potential difference between the non-selected potential and the potential of the modulation signal, is applied to the surface conduction electron-emitting devices in the unselected rows.
The surface conduction electron-emitting device has such a characteristic as to emit electrons only when the voltage applied to the device exceeds a threshold value, and also has such a characteristic that each of the device current (current flowing through the path between the two electrodes of the device) and the electron emission current (electron beam output intensity) increases monotonously with respect to the voltage applied to the device.
Therefore, the following statements can be obtained: if Ve, Vs, and Vns are set to suitable values, an electron beam having the desired intensity can be output only from the surface conduction electron-emitting devices in the selected row; if modulation signals varying in potential are applied to the column wiring lines, electron beams having different intensities are respectively output from the devices in the selected row; and since the response speed of the surface conduction electron-emitting device is high, the time during which the electron beam is output can be changed by changing the time for application of the modulation signal.
Various applications of multi-electron sources in which surface conduction electron-emitting devices are wired by passive matrix wiring, and in which the above-described various characteristics are utilized, are conceivable. For example, applications multi-electron source of this type to image display apparatuses using a method of suitably applying a voltage signal according to image information can be expected.
FIG. 16 is a schematic plan view of an image display apparatus in which surface conduction electron-emitting devices are wired by passive matrix wiring.
Referring to FIG. 16, the image display apparatus has a substrate 7, an image display portion 1 formed by connecting a plurality of surface conduction electron-emitting devices 2 in matrix form by a plurality of row wiring lines 6 and a plurality of column wiring lines 5, scanning circuits 4 serving as a scanning means for performing scanning by selectively applying a selected potential to one of the plurality of row wiring lines 6 and by changing the selected row wiring one by one, and modulation circuits 3 serving as a modulation means for obtaining modulation signals by controlling and modulating outputs from a plurality of constant voltage supplies according to an input image signal and for applying the modulation signals to the plurality of column wiring lines 5.
FIG. 17 is a schematic perspective view of the structure of a main portion of the image display apparatus shown in FIG. 16.
There are provided a metal back 8, a phosphor layer 9, and a substrate 10. As described above, electrons are emitted from the surface conduction electron-emitting device 2 by applying the modulation signal Ve to the column wiring line 5 and the selected potential Vs to the row wiring line 6, respectively. An acceleration voltage Va is applied to the metal back 8 provided above the surface conduction electron-emitting device 2. Part of electrons emitted from the surface conduction electron-emitting device 2 are accelerated by the acceleration voltage Va to reach the phosphor layer 9. The phosphor layer 9 thereby emits light for forming an image.
Electron-emitting devices using an emitter cone and MIM-type electron-emitting devices are known as well as the surface conduction type. An arrangement in which an electroluminescence device is used as an image forming device is also known.
As an arrangement for driving image display apparatuses using such image forming devices, a matrix drive method is known. A plurality of scanning signal lines and a plurality of modulation signal lines form matrix wiring, and image forming devices are driven in such a manner that modulation signals are simultaneously or successively applied through the plurality of modulation signal lines to image forming devices to which a selected potential is applied through the scanning wiring to which a scanning signal (selected potential) is applied.
Several arrangements for applying a scanning signal and a modulation signal are also known. For example, an arrangement for applying a modulation signal at a constant current (causing a current to flow at a desired value) and an arrangement for applying a modulation signal at a constant voltage are known. For example, JP 9-319327 A discloses an arrangement using a combination of a current supply and a voltage supply. As modulation methods, an arrangement for modulating the wave height value of a modulation signal, an arrangement for modulating the pulse width of a modulation signal, and an arrangement for using wave height value modulation and pulse width modulation in combination are known.
A known art disclosed in JP 2000-310966 A relates to the present invention. In an image display apparatus in accordance with this art, two transistors are first turned on at the time of fall of a signal to cause an abrupt fall of the signal and one of the transistors is then turned off to cause the signal to fall moderately.
Disclosed in JP 5-232907 A is a reset circuit which can be used in an image display apparatus. In this reset circuit, a certain impedance value during operation is changed to a lower impedance value to reduce the peak current value.
Disclosed in JP 8-190878 A is an arrangement in which a termination circuit using a resistor, a voltage dividing circuit, or a clamp circuit using a diode is added to input and termination terminals in wiring to prevent an increase in voltage exceeding a rated limit.